L1 Symbol Sample : `drot`#

To demonstrate how the meson.build system will work, we will try to generate an openblas library which can be used to compile the following snippet:

#include <cblas.h>
#include <stdio.h>

int main() {
  int n = 4;
  double x[] = {1, 2, 3, 4};
  double y[] = {5, 6, 7, 8};
  double c = 0.5; // cosine of the angle
  double s = 0.5; // sine of the angle

  // Apply the rotation
  cblas_drot(n, x, 1, y, 1, c, s);

  // Print the results
  printf("Resulting vectors:\n");
  printf("x: ");
  for (int i = 0; i < n; i++) {
    printf("%f ", x[i]);
  }
  printf("\n");
  printf("y: ");
  for (int i = 0; i < n; i++) {
    printf("%f ", y[i]);
  }
  printf("\n");

  return 0;
}

Baseline `openblas`#

With system libraries this is a snap:

gcc drot_example.c -lopenblas -o drotex
./drotex
Resulting vectors:
x: 3.000000 4.000000 5.000000 6.000000
y: 2.000000 2.000000 2.000000 2.000000

Without a system openblas, this works out to:

gh repo clone openmathlib/openblas openblas_temp
cd openblas_temp
make -j$(nproc)
make PREFIX=./tmpmake install
gcc drot_example.c -o drotex "-I$(pwd)/tmpmake/include" "-L$(pwd)/tmpmake/lib" -lopenblas
./drotex
Resulting vectors:
x: 3.000000 4.000000 5.000000 6.000000
y: 2.000000 2.000000 2.000000 2.000000

`meson.build` Outline#

As discussed in the roadmap, we need:

$GITROOT :: Where the library is declared
interface :: Where the prefixed symbols c$BLAS_SYM are named
kernel :: Where the implementation is $BLAS_SYM

Whittling flags#

By inspecting make logs, we can get the full set of flags for the interface symbol , cblas_drot in this case are:

'-O2',
'-DSMALL_MATRIX_OPT',
'-DMAX_STACK_ALLOC=2048',
'-Wall',
'-m64',
'-DF_INTERFACE_GFORT',
'-fPIC',
'-DSMP_SERVER',
'-DNO_WARMUP',
'-DMAX_CPU_NUMBER=12',
'-DMAX_PARALLEL_NUMBER=1',
'-DBUILD_SINGLE=1',
'-DBUILD_DOUBLE=1',
'-DBUILD_COMPLEX=1',
'-DBUILD_COMPLEX16=1',
'-msse3',
'-mssse3',
'-msse4.1',
'-mavx',
'-mavx2',
'-UASMNAME',
'-UASMFNAME',
'-UNAME',
'-UCNAME',
'-UCHAR_NAME',
'-UCHAR_CNAME',
'-DASMNAME=cblas_drot',
'-DASMFNAME=cblas_drot_',
'-DNAME=cblas_drot_',
'-DCNAME=cblas_drot',
'-DCHAR_NAME="cblas_drot_"',
'-DCHAR_CNAME="cblas_drot"',
'-DNO_AFFINITY',
'-DDOUBLE',
'-UCOMPLEX',
'-DCBLAS'

Which can be broken into a few different categories.

Common Configuration Flags#

Flags which are set for the build as a whole.

SMALL_MATRIX_OPT :: Which enables, as the name suggests a set of additional, optionally implemented kernels for interfaced symbols
MAX_STACK_ALLOC :: Defaults to 2048, detailed here and here

Based on the actual Fortran compiler used, the interface definitions need to be defined as well.

F_INTERFACE_GFORT, F_INTERFACE_INTEL, F_INTERFACE_G95 :: Indicates use of GNU Fortran interface naming conventions. Specific setup in Meson might be needed based on project requirements for Fortran interoperability.

Along with the symbol precision settings:

-DBUILD_SINGLE=1, -DBUILD_DOUBLE=1, -DBUILD_COMPLEX=1, -DBUILD_COMPLEX16=1 :: Indicate which data types (single, double, complex, double complex) to build. These can be configured in Meson using configuration_data() objects for preprocessor definitions.
-DDOUBLE, -UCOMPLEX :: Indicate building with double precision and excluding complex number support. Managed in Meson with conditional compilation flags or preprocessor symbols using add_project_arguments().

With some affinity and parallel settings as well.

SMP_SERVER :: Enables SMP (Symmetric Multiprocessing) server mode, affecting multi-threading and parallel computation. Thread handling in Meson may require specific target properties related to threading.
NO_WARMUP, MAX_CPU_NUMBER=12, MAX_PARALLEL_NUMBER=1 :: Control aspects of parallel execution and resource allocation, managed through add_project_arguments() in Meson for compile-time definitions.
NO_AFFINITY :: Disables processor affinity. System-specific setup or dependencies might be required in Meson for thread affinity management.

Standard build flags#

These have direct meson builtin base option equivalents:

-O2 :: Specifies the optimization level. Controlled in Meson through the buildtype or optimization options, where -O2 corresponds to buildtype=release or optimization=2.
-fPIC :: Enables Position Independent Code, which is a default in Meson for shared libraries.
-Wall :: Activates all compiler warnings, aligning with warning_level=2 or higher.

Hardware conditionals#

These depend on detecting the appropriate hardware.

-msse3, -mssse3, -msse4.1, -mavx, -mavx2 :: These flags activate optimizations for Intel’s SSE3, SSSE3, SSE4.1, AVX, and AVX2 instruction sets, respectively.

We can detect and apply through the use of meson.get_compiler('c').has_argument() to conditionally add them based on compiler support.

Symbol specific flags#

These are first unset, and then set. These flags unset certain preprocessor definitions, potentially to avoid predefined naming schemes conflicting with OpenBLAS’s custom configurations.

ASMNAME, ASMFNAME, NAME, CNAME, CHAR_NAME, CHAR_CNAME

One approach to this is to set them in a configuration object, as is done by the CMakelist files, or to directly use c_args.

Putting it together#

At this point, a simplified openblas library can be built up:

# ...
_inc = include_directories('.')
subdir('interface')
subdir('kernel')
_openblas = static_library('openblas',
                    link_whole: [ _interface, _kern])
# ...
# view targets via meson introspect bbdir --targets

With the relevant c_args as is done in this commit. The Meson build can proceed.

gh repo clone openmathlib/openblas openblas_meson
cd openblas_meson
git checkout fa1f52ff7b13e95f2b31096dd65f001ba87b4b3f
meson setup bbdir
meson compile -C bbdir
gcc trial.c -o drotex "-I$(pwd)/" "-L$(pwd)/bbdir" -lopenblas
Resulting vectors:
x: 3.000000 4.000000 5.000000 6.000000
y: 2.000000 2.000000 2.000000 2.000000

Perhaps more pertinently, we can view the actual symbols so generated:

❯ nm -gC bbdir/libopenblas.a | grep drot
bbdir/interface/libcblas_drot.a.p/rot.c.o:
0000000000000000 T cblas_drot
                 U drot_k
bbdir/kernel/libdrot_k.a.p/arm_rot.c.o:
0000000000000000 T drot_k

So in this vein we may now proceed building all the L1 symbols.

L1 Symbol Sample : drot#

Baseline openblas#

meson.build Outline#